Ceramic materials generally possess several advantageous properties. For example, components or parts constructed from ceramic materials generally are very hard, have a relatively high resistance to wear, corrosion, thermal stress, and compressive stress, are generally nonconductive, and may possess other properties that are advantageous for particular applications. However, ceramic components and parts also tend to be brittle and are capable of withstanding only relatively small tensile stresses. Consequently, the use of ceramic parts has been primarily limited to applications where the ceramic part is subjected to little or no tensile loads.
While many different machines and devices could benefit from a part or component that is hard, that exhibits high resistance to wear, corrosion, thermal stress, and compressive stress, and that is nonconductive, ceramic has not been a feasible option for use in these machines and devices because of its relative inability to withstand tensile stresses. For example, in high-pressure fuel pumps, such as the fuel pumps used in common rail fuel injection systems to generate rail pressures up to and even beyond 190 MPa, the use of a plunger or piston that is hard, that has high resistance to wear, corrosion, thermal stress, and compressive stress, and that is nonconductive would be beneficial. However, manufacturers have had difficulty making use of ceramic plungers because the ceramic plungers are exposed to excessive tensile stresses which cause the plungers to prematurely fail.
Various retention assemblies that are used to hold a piston within a retainer assembly in a pump or within a rod in a hydraulic cylinder are known. One example of such a retention assembly is described in U.S. Pat. No. 3,654,839, issued Apr. 11, 1972 (“the '839 patent”). The retention assembly of the '839 patent includes a split retainer that has a rib that engages a grooved portion of a rod and a flange that engages a groove in a piston. A circumferentially interrupted band surrounds the split retainer and serves to hold the retainer in an operative condition prior to the insertion of the rod and piston assembly into a cylinder. The engagement of the rib with the groove in the rod and the engagement of the flange with the groove in the piston serve to retain the rod within the piston. Although the retention assembly described in the '839 patent represents a simple way to retain the rod within the piston, it may not be suitable for applications where it is important to minimize the tensile stress experienced by the member being retained (in this case, the rod) because the retention assembly serves to rigidly couple the piston to the rod and does not provide a stress reduction mechanism.
It would be advantageous to provide a relatively simple, reliable, durable, and inexpensive retention system that could effectively hold a ceramic element or plunger and at the same time reduce the magnitude of tensile stresses experienced by the plunger to extend the life of the plunger.